Added strict validation for Image sampling

holoviews/element/raster.py

@@ -1,4 +1,6 @@
+import sys
 from operator import itemgetter
+
 import numpy as np
 import colorsys
 import param
@@ -260,6 +262,19 @@ def __init__(self, data, kdims=None, vdims=None, bounds=None, extents=None,
                 raise ValueError("Input array has shape %r but %d value dimensions defined"
                                  % (self.shape, len(self.vdims)))
 
+        xvals = np.unique(np.diff(self.dimension_values(0, expanded=False)))
+        if len(xvals) > 1 and np.abs(xvals.min()-xvals.max()) > sys.float_info.epsilon*10:
+            raise ValueError("%s dimension %s is not evenly sampled, "
+                             "please use the QuadMesh element for "
+                             "unevenly or irregularly sampled data." %
+                             (type(self).__name__, self.get_dimension(0)))
+        yvals = np.unique(np.diff(self.dimension_values(1, expanded=False)))
+        if len(yvals) > 1 and np.abs(yvals.min()-yvals.max()) > sys.float_info.epsilon*10:
+            raise ValueError("%s dimension %s is not evenly sampled, "
+                             "please use the QuadMesh element for "
+                             "unevenly or irregularly sampled data." %
+                             (type(self).__name__, self.get_dimension(1)))
+
 
     def __setstate__(self, state):
         """